Device for producing plastic molded sheets

ABSTRACT

A device for producing synthetic plastic molded sheets including a mold rotatable about at least one axis and receiving a thermoplastic synthetic resin powder which is sequentially heated and cooled by liquid heating and cooling medium admitted into a hollow chamber of the mold, and a housing formed with a housing wall provided with a plurality of bulges for compensating thermal stresses resulting from different materials of the housing wall and a wall of the chamber.

CROSS REFERENCE TO RELATED APPLICATION

This a national phase application of PCT/EP 92/02734 filed Nov. 27, 1992and based, in turn, on German application P41 42 109.4 filed Aug. 19,1992 under the International Convention. This invention relates to adevice for producing plastic molded sheets by alternatively heating andcooling mold surfaces.

BACKGROUND OF THE INVENTION

A device of this type is known from German Open Application 34 17 727,in which mold or the casting form is heated in a furnace and afterreaching the operating temperature is fed to the next operating station,the changing station in which the mold is coupled with a receptaclecontaining a liquid thermoplastic synthetic resin.

The heating of the mold with hot circulating air requires a high energyexpense and is time consuming, since apart from the quantities of airrequired to heat the molding, also associated holding elements must beheated. The heating with circulating air also has the drawback thatresidue particles from previous operating steps pass from the mold whichhas been cooled and from which the plastic molded sheet has beenseparated into the circulating air and can be deposited again on themolding surfaces of the mold.

From French Patent 1 600 351 it is also known, further, to heat abiaxially rotatable closed mold from the exterior by means of aninfrared radiator so that the pulverulent plastic found in the moldingis distributed uniformly over the inner surface of the mold, is theremelted and, upon cooling down of the mold, can be removed as a plasticmolded sheet. This type of operation also requires a high cost and istime consuming with respect to the sequence of heating and cooling.

OBJECTS OF THE INVENTION

It is therefore the object of the present invention to provide a device;with a rapid succession between heating and cooling of the mold; andanother object is to provide the mold which can withstand rapidlyalternating thermal expansions.

SUMMARY OF THE INVENTION

According to the invention, the device includes the walls which arecomprised of nongalvanically formed material of the hollow chamberfillable with the heating and cooling medium and which have bulges forcompensating the thermal expansion.

In a device for producing synthetic plastic molded sheets by means of amold rotatable about one or more axes of rotation, in which athermoplastic synthetic resin powder melts upon a heated mold surface inthe form of a film and after cooling of the mold wall can be removed inthe form of a plastic molded sheet, the heating and cooling beingeffected in alternating sequence by means of liquid heating and coolingmedium admitted into a hollow chamber of the mold. To compensate forthermal stresses between the housing walls defining the hollow chamberand the mold wall, bulges are provided in the housing wall to compensatestresses. The thermal stresses arise primarily because of the differentmaterials of the mold wall and the housing wall. The mold wall iscomprised of a galvanic material, for example, a copper-nickel alloy,while the housing wall is comprised of normal steel sheets.

The device is also formed with a closed mold chamber and two axes ofrotation.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become morereadily apparent from the following description, reference being made tothe following single drawing in which the sole FIG. is a partialsectional view of the deice according to the invention.

SPECIFIC DESCRIPTION

The drawing shows a mold 1 comprised of a mold wall 2 which is composedof a material formed in a galvanic process, for example a nickel-copperalloy. According to this process, the mold surface 3 can be providedwith a pitting as, for example, is customary for dashboards of anautomobile.

Behind the mold wall 2 there is provided a hollow chamber 4 which ispartly enclosed by the mold wall 2 and in the remainder by the housingwall 5 which is a steel sheet. The housing wall 5 which is sealinglyfashioned on the mold wall 2 comprises side steel sheet walls in theform of inwardly curved bulges 7 and a bridging steel sheet wallextending between the side walls and spaced from the mold wall to form achamber 4, said bridging steel sheet wall including bulges 6 wherein theapexes of the bulges 6 face away from the mold wall 2. The housing wall5 further comprises a connecting fitting 8 for connection with areceptacle containing the heating and cooling media to be delivered tothe chamber 4. The heating and cooling media comprise preferably oil.

The mold 1 is connected with a plastic receptacle 9 which contains thefluent thermoplastic synthetic resin powder 10. The powder receptacle 9,is for example, connected releasably with the mold 1 by means of a flaphinge 11 whereby the interior of the mold 12 can be accessible. The mold1 is held in a support frame 13 in which it is rotatable about a firstaxis 14 of rotation. The support frame 13, in turn, is rotatable about asecond axis 15 of rotation perpendicular to the first rotation axis 14such that the mold 1 is biaxially rotatable.

In operation, usually the hollow chamber 4 of the mold with which thepowder receptacle 9 is connected, is filled with heating medium, uponthe mold 1 as rotated about the two axes 14 and 15 of rotation. As aresult of this biaxial rotation, the thermoplastic synthetic resinpowder is uniformly distributed over the mold surface 3 and melts toform a film thereon. Then the hollow chamber 4 is filled with thecooling medium whereupon the film layer on the mold surface 3 issolidified to a synthetic resin so that upon swinging away of the powderreceptacle 9, of the mold 1, this synthetic resin sheet can be removed.

The thermal expansion which occurs in the mold 1 as a result of thealternating filling with heating and cooling medium and which alsoarises because of the different material characteristics of the moldwall (nickel-copper alloy) and the hollow chamber housing steel sheet iscompensated by the bulges 6, 7 formed in the housing wall 5.

I claim:
 1. A device for producing plastic molded sheets, the devicecomprising:a closable mold cavity formed with a mold wall made of anickel-copper alloy and having a molding surface; means for transferringa synthetic resin into contact with said surface; a housing providedalong the mold wall and formed with:side steel sheet walls sealedagainst the mold wall, and a bridging steel sheet wall extending betweenthe side walls and spaced from the mold wall, the steel sheet walls ofthe housing and the mold wall forming thereby a chamber therebetween;means for alternatively filling the chamber with liquid heat medium andliquid cooling medium; actuating means for rotating the housing and themold cavity to cause the synthetic resin to melt on the molding surfaceupon delivering the heating medium into the chamber and forming auniformly thick film of the synthetic resin upon cooling; means forcompensating different degrees of longitudinal expansion between themold wall and the housing walls upon heating and cooling of the moldingsurface and including a plurality of bulges formed on the side steelsheet walls and on the steel sheet bridging wall of the housing, saidbulges imparting a shape to said chamber; and means for opening the moldcavity to remove the film from the molding surface upon solidifying ofthe synthetic resin.
 2. The device defined in claim 1 wherein the bulgesformed on the side walls are curved inwardly toward one another.
 3. Thedevice defined in claim 1 wherein the mold cavity is rotatable about twomutually perpendicular axes.
 4. The device defined in claim 1 wherein atleast one of the bulges formed on the bridging wall of the housing isprovided with an apex facing away from the mold wall.